IMPORTANT: On 1 September 2017, Celotex took the precautionary measure to temporarily suspend the supply of Celotex FR5000, Celotex CG5000, Celotex CF5000 and Celotex SL5000 while we investigate the results of recent tests (Parts 6 and 7 of British Standard 476). Materials relating to these products are for information only.

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Influencing factors shaping and driving insulation choice for full fill cavity wall

CF5000_0002 (FINAL)

Today sees the launch of Celotex CF5000, a brand new full fill cavity wall solution from Celotex, and so it seems right to look at the influencing factors that drive the insulation choice for this specific application.

Part L1A and FEES

Over the last ten years there have been a number of successive changes to Approved Document Part L1A. Part L1A is concerned with how much energy a new residential building uses and such has a direct impact on the fabric of the building and its ability to conserve energy.

The most recent changes in 2013 included a new metric called FEES. This focuses on improving the fabric of the building to reduce energy consumption or in layman’s terms how often you switch your heating on.  The introduction of FEES meant new homes built in England require a stronger fabric performance to comply with SAP.

SAP compliance is a requirement of Part L1A

So what is FEES?

FEES stand for Fabric Energy Efficiency Standard. It measures the energy efficiency of the building envelope as a whole. It means buildings by design have better U-values through the walls, roof and floors. Heat loss is designed out of junctions around walls and the building has better air tightness. A strong fabric performance conserves energy so that the rooms stay at a steady temperature providing good levels of thermal comfort using very little energy.

Approved Document C

Technically we are referring to Approved Document C Part 2. This document sets out design considerations on how to keep a building dry.  It has a section on walls and in particular a wind driven rain index for different areas of the country commonly understood as exposure zones. It divides England, Scotland and Wales into four exposure zones ranging from very severe to sheltered.

Local Building Control (LBC) is the authority on this subject unless the project is built to NHBC technical standards.

Under LBC, full fill cavity wall insulation can be used in all four exposure zones. However, it’s true to say the risk of wind driven rain in severe exposure zones is designed out with a combination of insulation type and either clear cavities or external cladding types and mortar joints.

NHBC technical standards indicate full fill cavity wall insulation is not permitted in severe exposure zones and Scotland. I think it’s true to say in summary exposure to wind driven rain directly influences insulation type and to a degree cavity wall design and construction.

BBA Certificate

Insulation being used in a cavity wall whether it be ‘built in’ or ‘blown’ must have a BBA Certificate. Insulation within a cavity wall and BBA Certification is a requirement as written in Approved Document C part 2. Why? Quite simply full fill cavity wall insulation must pass a wet wall test which is witnesses and assessed by the BBA. Partial fill by design will have a residual clear cavity which along with cavity trays and weep holes manages excess moisture so that it drains safely away from the internal leaf.

So to summarise:

  • New residential homes built must have a stronger fabric performance to comply with SAP and Part L1A 2013
  • Use the correct insulation and application for the exposure zone
  • Must be BBA approved

Translated into design considerations Housebuilders are challenged with designing the most economic recipe that optimises technical build performance to comply with SAP and give commercial value, at the same time, using materials suitable for the exposure zone.

 A full fill cavity wall solution

Walls are key to the building footprint, so if the cavity is widened to accommodate thicker insulation this will impact plot efficiencies. Not to mention the requirement of longer wall ties and sized lintels and cavity closers etc.

Celotex CF5000 provides a high performance full fill cavity wall solution to complete our cavity wall portfolio. 97mm CF5000 in a 100mm cavity gives 0.18W/m²K, and therefore improves the thermal performance without the need to widen the cavity. Space is optimised to ensure plot efficiencies, and such, provides a viable commercial solution while ticking a technical box.

Celotex CF5000 full fill insulation

Find out more about Celotex CF5000 by visiting